The invention relates to the application of magnetoimpedance, also called here RMS (resistive magnetic saturation), in the field of sensors.
More precisely, the invention relates here to the use of this magnetoimpedance on a contactless position sensor, and to the sensor itself.
The physical phenomenon involved here is, in general, the following:                an electrical conductor through which an AC electrical current flows sees this current distributed around the periphery of the conductor.        
This phenomenon is commonly called the skin effect.
The depth of this skin is determined by the formula:
  δ  =            ρ                        πμ          0                ⁢                  μ          r                ⁢        f            where:                δ is the skin depth;        ρ is the resistivity of the conductor in ohms.meter;        μ0 is the magnetic permeability of free space (4π×10−7);        μr is the magnetic permeability of the material; and        f is the frequency in hertz.        
Thus, the more the frequency f increases, the more the skin depth δ decreases.
Moreover, the electrical resistance of an electrical conductor is given by the formula:
  R  =            ρ      ⁢                          ⁢      L        A  where:                R is the resistance of the conductor in ohms;        ρ is the resistivity of the conductor in ohms.meter;        L is the length of the conductor in meters; and        A is the cross-sectional area of the conductor.        
It should be noted that, in such a skin effect phenomenon, when the frequency f increases for a given electrical conductor (all other things being equal) the area A decreases and therefore the measured resistance R greatly increases.
If a magnetic field is applied to the electrical conductor made of an appropriate material, this modifies the magnetic permeability (μr) of the material.
This has the effect of making the measured resistance R drop compared with the same conductor not subjected to the external magnetic field in question.
This phenomenon has already been used to measure, typically with great precision, absolute magnetic fields, and sensors operating on the principle of magnetoimpedance, and especially on giant magnetoimpedance, have been developed. They operate at very high frequencies (greater than 1 GHz in the case of giant magnetoimpedance) and in particular use amorphous materials for forming the electrical conductor serving as sensitive element.
The problem posed here is that of how to widen the field of application of magnetoimpedance, on the basis of the abovementioned physical phenomenon, without necessarily having to measure very precisely the magnetic fields in question and without necessarily incurring the high costs imposed hitherto, in particular in the case of the aforementioned sensors, especially those developed in relation to giant magnetoimpedance.